This invention relates to non-metallic shotshells and more particularly to all plastic shotshells.
Conventional all-plastic shotshells all suffer from a common problem. They do not feed reliably from semi-automatic shotguns but instead suffer rim shear problems. A solution to this problem is needed. A one-piece, hard plastic head may be molded using nylon, polycarbonate and similar resins on one end of an extruded polyethylene tubing to form an all-plastic cartridge case and the molded hard head would, prior to firing, adhere to the tubing and withstand (for example, in 12 gauge shells) 100 or more pounds of head pulling forces. However, when such hard-headed shotshells are fully loaded into shotshell rounds and are test fired in pressure barrels or guns, the heads become loose from the tubing and often fall off. It appears to applicants that, upon firing, the adhesion of the hard nylon and such other plastic heads to polyethylene tubing is insufficient to withstand firing forces as the two plastic materials are incompatible, being immiscible and so do not form a strong enough initial chemical bond. Even the conventional pretreatment of the polyethylene tubing with chromic acid, chlorine or flame does not improve the adhesion of the hard head plastic to the polyethylene tubing upon firing. Thus, plastic shotshell manufacturers have uniformly only used head materials which are chemically similar to the plastic tube, thus sacrificing rim quality in order to have an adherent head to prevent gas leakage. Also, it has traditionally been felt by ammunition makers that hard plastic heads would be too brittle at low temperatures to withstand high firing pressures and would result in cracked heads, a critical defect.
The present invention solves the above problems by providing a cartridge case without metallic reinforcement portions, comprising an exterior tubular body of plastic having a base end; an internal adherent plastic basewad molded to the inside surface of the base end of said body and having an axial opening adapted to receive a primer and having one or more interlock channels therein; an exterior hard, tough plastic rim molded into mechanically interlocked attachment to said interlock channels of said basewad, said rim being of a material chemically dissimilar from and not chemically adherent to either of said tubular body and basewad.